New Flyer Articulated Low Floor Bus

After an initial successful test of one hybrid artic, Metro purchased a fleet of these buses from New Flyer of America in 2004 to replace the Breda dual power buses operating on tunnel routes. These buses are based on the standard New Flyer low floor artic, but have an Allison parallel hybrid drive system instead of a conventional automatic transmission. The Allison system consists of the hybrid drive unit containing two electric motors/generators, planetary gears and clutches, a roof-mounted battery pack, an inverter, and a system controller.

The hybrid buses delivered in 2002 and 2004 have Caterpillar C9 diesel engines. The hybrid buses delivered in 2008 have Cummins ISL diesel engines. The parallel nature of the Allison system means that at low speed the bus is largely electrically driven, while at medium speeds it is a blend of mechanical and electric, and at high speeds it is mostly mechanical. Electric power is provided by the battery pack, and this is charged by the hybrid drive motors acting as generators while the bus is decelerating or braking.

Use of the hybrid drive improves fuel economy compared to straight diesel, and reduces emissions because the electric drive is taking over part of the propulsion duties of the diesel engine.